1. Field of the Invention
Embodiments of the present invention generally relate to solar cells and methods for forming the same. More particularly, embodiments of the present invention relate to methods for manufacturing thin-film solar cells with high conversion efficiency.
2. Description of the Related Art
Solar cells convert solar radiation and other light into usable electrical energy. The energy conversion occurs as the result of the photovoltaic effect. Solar cells may be formed from crystalline material or from amorphous or microcrystalline materials. Generally, there are two major types of solar cells that are produced in large quantities today, which are crystalline silicon solar cells and thin film solar cells. Crystalline silicon solar cells typically use either mono-crystalline substrates (i.e., single-crystal substrates of pure silicon) or a multi-crystalline silicon substrates (i.e., poly-crystalline or polysilicon). Additional film layers are deposited onto the silicon substrates to improve capture of light, form the electrical circuits, and protect the devices. Suitable substrates include glass, metal, and polymer substrates. It has been found that the properties of thin-film solar cells degrade over time upon exposure to light, which can cause the device stability to be less than desired. Typical solar cell properties that may degrade are the fill factor (FF), short circuit current, and open circuit voltage (Voc).
Thin film silicon solar cells have gained a significant market share due to low-cost, large-area deposition of the amorphous-microcrystalline silicon absorber layers. Thin-film solar cells use thin layers of materials deposited on suitable substrates to form one or more p-n junctions. Generally, different material layers perform different functions formed in the solar cells. In some instances, some material layers may server as a light absorber layer that may have high light-trapping effect to absorb light in the absorber layer to generate high current. In contrast, some material layers are configured to reflect and scatter light to the solar cells formed on the substrate so as to assist light retaining in the solar cell for a longer time for current generation. However, absorption loss may often occurs when light transmitting through these reflective material layers, thereby adversely reducing overall electrical performance and conversion efficiency of the solar cell junctions formed on the substrate. To expand the economic uses of solar cells, efficiency must be improved. Solar cell efficiency relates to the proportion of incident radiation converted into useful electricity. To be useful for more applications, solar cell efficiency must be improved beyond the current best performance of approximately 15%. With energy costs rising, there is a need for improved thin film solar cells and methods and apparatuses for forming the same in a factory environment.